1. Field of the Invention
The present invention relates to a microstrip line, a resonator element, a filter, and a high-frequency circuit that utilize the microstrip line, and to an electronic circuit, circuit module, and communications device that utilize the resonator device, filter, and high-frequency circuit.
2. Description of the Related Art
In small electronic devices having microwave or milliwave circuitry, a microstrip line, as shown in FIG. 23, is generally used as a transmission line for transmitting signals having frequencies in the microwave or milliwave band. FIG. 23 shows a portion of a microstrip line 1 that includes a dielectric substrate 2, a ground electrode 4 provided on the back 3 of the dielectric substrate 2, and a flat line electrode 6 provided on the front 5 of the dielectric substrate 2.
It is well-known that most of the line transmission loss in the microstrip line 1 is conductor loss attributable to the concentration of current at the edges 7 and 8 of the line electrode 6, and that an xe2x80x9cedge effectxe2x80x9d exists (R. A. Pucel, xe2x80x9cLosses in Microstrip,xe2x80x9d IEEE Trans. on MTT, Vol. MTT-16, June 1968, pp. 342-350). Conductor loss is greater when the line electrode 6 is narrow. Consequently, it is difficult to produce an electronic circuit having highly integrated microstrip lines 1 and very narrow line electrodes 6.
An effective way to improve this situation is to increase the thickness of the line electrode 6 and to reduce the current density at the edges 7 and 8 of the line electrode 6. FIGS. 24A and 24B are graphs of the transmission characteristics (calculated) for the microstrip line 1 when the thickness of the line electrode 6 is varied. In FIG. 24A, Qo is the resonance when the microstrip line 1 is cut to a specific length and made into a resonator. The value of Qo increases as the conductor loss of the line electrode 6 decreases. In FIG. 24B, Zo is the characteristic impedance of the microstrip line 1, and Koff is the effective dielectric constant of the dielectric substrate 2.
The microstrip line 1 used in the calculation of transmission characteristics for FIGS. 24A and 24B was configured such that the dielectric constant of the dielectric substrate 2 was 38, the thickness of the dielectric substrate 2 was 300 xcexcm, and the width of the line electrode 6 was 20 xcexcm. As is clear from FIGS. 24A and 24B, when the thickness of the line electrode 6 is varied over a range of 1 xcexcm to 25 xcexcm, the characteristic impedance Zo and the effective dielectric constant Keff changes very little. In contrast, the Qo value increases in proportion to the thickness of the line electrode 6, which indicates that the conductor loss decreases.
A problem, however, is that when the thickness of the line electrode 6 is increased, the precision of the electrode pattern of the electronic circuit decreases. Consequently, there have been attempts at decreasing the edge-effect without increasing the thickness of the line electrode 6. The following is a conventional example of such attempts.
The microstrip line shown in FIG. 25 is discussed in xe2x80x9cMultilayered MMIC, V-Groove Microstrip Line Characteristics,xe2x80x9d by Hasegawa et al., 1990 Electronic Information Communications Society, National Fall Conference, lecture C-55. A microstrip line 10 has a V-shaped groove 13 provided on the front 12 of a dielectric substrate 11, and a V-shaped line electrode 14 having a crease 15 is provided in the middle of this groove 13. As a result, the electric field is concentrated between the V-shaped lower end portion of the line electrode 14 and a ground electrode 16 provided on the back of the dielectric substrate 11, thereby reducing the concentration of current at the edges 17 and 18 of the line electrode 14.
Japanese Laid-Open Patent Application 10-313203 discloses a microstrip line in which a groove is provided in a dielectric substrate to reduce the transmission loss of high-frequency signals. As shown in FIG. 26, this microstrip line 20 is designed such that a flat line electrode 23 is provided on the front 22 of a dielectric substrate 21, a V-shaped groove 25 is provided on the back 24 of the dielectric substrate 21 at a location across from the line electrode 23, and a ground electrode 26 is provided to include the groove 25. With this configuration, an electric field is concentrated between the line electrode 23 and the ground electrode 26 in the V-shaped portion 27 of the ground electrode 26, which reduces the concentration of current at the edges 28 and 29 of the line electrode 23.
Furthermore, Japanese Laid-Open Patent Application 8-288463 discloses a microstrip line in which the transmission loss of the line is decreased by utilizing a skin effect. As shown in FIG. 27, this microstrip line 30 includes a ground electrode 33 provided on the back 32 of a dielectric substrate 31, and a line electrode 38 provided on the front 34 of the dielectric substrate 31, on the sides 35 and 36 of the line electrode 38 a plurality of grooves 37 are provided. This expands the surface area of the sides 35 and 36 of the line electrode 38, thereby increasing surface current at the sides 35 and 36 and reducing transmission loss.
Nevertheless, with the microstrip line 10 in FIG. 25, it is difficult to form the V-shaped groove 13 with high precision in the dielectric substrate 11, and with the microstrip line 20 in FIG. 26, it is difficult to machine the V-shaped groove 25 with high precision in the dielectric substrate 21. Moreover, the configurations of these microstrip lines 10 and 20 do not provide the benefit of greatly increasing the Qo value of the microstrip line. With the microstrip line 30 in FIG. 27, the method of forming the line electrode 38 is complicated and the manufacturing costs are high.
To overcome the above-described problems, preferred embodiments of the present invention provide a microstrip line that reduces the edge effect of the line electrode, a high frequency circuit and a resonator device including the microstrip line that reduces the edge effect of the line electrode, a filter including the resonator device, an electronic circuit constituted including this filter, a circuit module including this electronic circuit, and a communications device including these devices.
A microstrip line according to a second preferred embodiment includes a dielectric substrate, a ground electrode provided on the back of the dielectric substrate, and a line electrode provided on the front of the dielectric substrate, and edge electrodes provided at the edges on both sides of the line electrode. The edge electrodes extend in a direction that is substantially perpendicular to the front of the dielectric substrate.
With the microstrip line according to the second preferred embodiment, the reduction in transmission loss in the microstrip line is proportional to the height of the edge electrodes. However, when short edge electrodes are provided on the line electrode, the line electrode and edge electrodes can be provided with high precision using thin film forming methods.
A microstrip line according to a third preferred embodiment includes a dielectric substrate, a ground electrode provided on the back of the dielectric substrate, and a line electrode provided on the front of the dielectric substrate, and edge electrodes provided at the edges on both sides of the line electrode. The edge electrodes are preferably arranged at an angle with respect to the front of the dielectric substrate.
With the microstrip line according to the third preferred embodiment, even though the edge electrodes are arranged at an angle to the front of the dielectric substrate over their entire length, there is a reduction in the conductor loss of the microstrip line, corresponding to the length from the front of the dielectric substrate to the tops of the edge electrodes, and the edge effect of the microstrip line is greatly reduced.
A microstrip line according to a fourth preferred embodiment further includes a pair of reinforcing components made of a material having a small dielectric loss and provided on the front of the dielectric substrate to support the edge electrodes.
The edge electrodes are provided utilizing the sides of the reinforcing components, and because the edge electrodes are structurally stable, they can be made taller than the thickness of the line electrode, allowing the effect of reducing transmission loss to be further improved. Also, a material with a dielectric loss that is about the same as or considerably less than the dielectric loss of the dielectric substrate is used as an insulating material that forms the reinforcing components, which prevents the dielectric loss from increasing due to the addition of the reinforcing components.
According to a fifth preferred embodiment, the reinforcing components are preferably defined by insulating films made of a resin material. This is particularly effective when it is necessary to suppress an increase in dielectric loss in the microstrip line while performing fine machining at a narrow line electrode width.
According to a sixth preferred embodiment, the reinforcing components may be made of a ceramic material. This is particularly effective when a wide line electrode and tall edge electrodes are provided to achieve a high Q value of the microstrip line. For instance, it is possible to produce a microstrip line having a large strip conductor in which the line electrode width is approximately 140 xcexcm and the edge electrodes are approximately several hundred microns tall. This further reduces transmission loss.
The microstrip line according to a seventh preferred embodiment further includes a line groove provided between the pair of reinforcing components, with the front of the dielectric substrate defining the bottom of the groove, this line groove has sides that are substantially perpendicular to the front of the dielectric substrate. The line electrode is provided at the bottom of the line groove, edge electrodes are linked along the entire length of the line electrode, and the edges of the line electrode are provided on the sides of the line groove. This makes it easier to form the strip conductor.
The microstrip line according to a eighth preferred embodiment of the present invention further includes a line groove is provided between the pair of reinforcing components, with the front of the dielectric substrate defining the bottom of the groove, and the line groove has sides that are inclined with respect to the front of the dielectric substrate. The line electrode is provided at the bottom of the line groove, edge electrodes that are linked along the entire length of the line electrode, and the edges of the line electrode are provided on the sides of the line groove. This makes it easier to form the strip conductor.
The microstrip line according to a ninth preferred embodiment includes edge electrodes having a flat portion extending substantially parallel to the front of the dielectric substrate along the top of the reinforcing components. This enhances the dimensional precision of the edge electrodes.
The microstrip line according to a tenth preferred embodiment includes a portion of the line electrode extending between the reinforcing components and the front of the dielectric substrate. This enhances the dimensional precision of the line electrode.
The microstrip line according to an eleventh preferred embodiment further includes a flat electrode that links the upper ends of the pair of edge electrodes. As a result, the strip conductor has a hollow construction, and it is possible to increase the surface current of the strip conductor.
The microstrip line according to a twelfth preferred embodiment wherein a space surrounded by the line electrode, the flat electrode, and the edge electrodes are filled with a filler having a small dielectric loss tangent. This makes it easier to produce a strip conductor having a transmission loss that is about the same as that of the strip conductor of the eleventh preferred embodiment, in which the interior was hollow, while still reducing the edge effect.